Overview of the chemical composition and its evolution for a 100 M_⊙ model calculated from the onset of core H burning until core He exhaustion for Z_⊙ (upper left), Z = 0.004 (upper right), Z = 0.002 (lower left), and Z = 0.0002 (lower right). The shaded region illustrates the interior composition at the end of core He burning, while the unshaded region shows the surface abundances of each isotope with time evolving from right to left as mass is lost through winds. The vertical black solid line denotes the end of core He burning, while the vertical magenta solid line shows core H exhaustion.